During the production of paper from cellulosic fibrous material pulp, it is typically necessary to add specific chemicals to the pulp for performing various operations, or to wash out the chemicals from the pulp. The addition of chemicals may be effected by displacement flow through the pulp mass, and washing is typically performed by one or more sequences of displacement of wash liquid through the pulp mass followed by pressing of the wash liquid from the mass.
Conventional wash presses typically require dilute pulp supplied in the consistency range of about 2 to 5%. The dilution allows the pulp to spread evenly onto the wash press filter media to form a web or mat. The filter media is conventionally a perforated rotating drum or moving belt. The pulp is thickened on the filter media to about 10-16% consistency usually by application of pressure to the mat or by vacuum draw. After thickening, washing of the chemicals from the pulp mat is accomplished by forcing wash water through the mat (displacement) using hydraulic pressure or drawing wash water through with a vacuum. Finally, the mat is compressed by the wash press to high consistency of 30 to 50% to achieve a high total washing efficiency. The conventional method of compressing the mat for pressing is to pass it through the nip of rollers or press on it with a belt moving the same speed as the mat.
According to the present invention, many difficulties and inconveniences associated with the prior art wash presses may be eliminated while still providing effective treatment of the pulp. The invention can be used not only for washing of the pulp with a final step of pressing, but also for chemical treatment of the pulp. The invention effects the desired results in a simple manner and with a minimum of moving parts. According to the invention it is possible to supply pulp at a consistency range of about 2-16%, and preferably about 8 to 12% (that is medium consistency pulp) which eliminates the need for thickening at the inlet, which in turn minimizes screen (filter) area. The device according to the invention can compress the pulp without the need of a nip, roll, or moving belt, and can eliminate the need to back wash the filter media for cleaning due to fibers stuck in the filter media. In conventional wash presses the mat moves at the same speed as the press roller belt so that the fibers are pressed firmly against the filter media and some fibers staple into the perforations of the filter media. According to the invention, however, during pressing, compressed pulp drags fibers from screen perforations, producing a self-cleaning effect.
According to one aspect of the present invention, a device is provided for liquid treatment of a suspension of cellulosic fibrous material (paper pulp) comprising the following elements: (a) A housing having an outer, essentially solid, wall; including a restricting adjustable portion. (b) Means defining a channel having a root wall and a pair of side walls with an open face opposite the root wall, the channel being positioned so that the open face thereof is adjacent the housing outer wall, and at least one of the walls is perforated. (c) Means for moving the root wall, and at least one of the side walls, with respect to the outer wall in the dimension of elongation of the channel. (d) Means for feeding material to be treated into the channel at one portion of the housing. (e) An outlet for passage of treated material out of the channel and the housing adjacent the restricting adjustable portion of the housing outer wall. (f) Means for introducing treatment fluid into the channel, between the means (d) and (e), through the housing outer wall, so that the treatment fluid passes through the material to treat it, and out perforations in at least one of the channel walls. And, (g) means for providing discharge of liquid from the housing that has passed through perforations in at least one of the channel walls.
The device according to the present invention operates on the same basic principle as the press illustrated and described in U.S. Pat. No. 4,534,868 (the disclosure of which is hereby incorporated by reference herein), as evidenced by the commercial product sold by Kamyr, Inc. of Glens Falls, N.Y. under the trademark "Ring".RTM.. During pressing, the channel perforated walls move faster than the compressed pulp and consequently the fibers do not staple into the perforations. Instead the compressed pulp drags fibers from the perforations producing a self-cleaning effect.
The means for introducing treatment liquid into the channel comprises a hollow distributor extending from the outer wall into the approximate center of the channel between the side walls, and comprises a pair of perforated side walls. The side walls are parallel to the channel side walls, both of which are preferably perforated while the root wall is not. The end wall of the distributor is closely spaced from the root wall and also is perforated. The housing outer wall is preferably arcuate, and the root wall is an arcuate wall of a rotor with the side walls extending radially outwardly therefrom, and a plurality of the distributors are provided along the housing outer wall circumferentially spaced from each other in the direction of movement of the channel.
The invention also relates to a method for treating a pulp suspension using an arcuate root wall rotatable about an axis and defining an open channel with a pair of side walls extending radially outwardly with respect to the root wall. At least one of the side walls is rotatable with the root wall and at least one of the channel defining walls is perforated. The method comprises the steps of continuously and progressively: (a) Rotating the root wall about an axis. (b) Introducing a suspension of cellulosic fibrous material at a consistency of about 2-16% by weight (preferably about 8-12%) into the channel. (c) Introducing treatment fluid into the suspension in a center portion of the channel so that the treatment fluid permeates the suspension. (d) Effecting removal of liquid from the channel through the perforated walls defining the channel to facilitate treatment and thickening of the suspension. And, (e) discharging suspension having a consistency greater than that of the introduced suspension (e.g. about 30-50%). Step (c) is preferably practiced by introducing treatment liquid in distributors extending into the channel from the open part thereof opposite the root wall so that the treatment liquid flows substantially uniformly into the suspension at all portions along the radial extent thereof. The treatment liquid preferably comprises a wash liquid, but may also be any of a wide variety of treatment chemicals depending upon the particular end use of the pulp.
It is the primary object of the present invention to provide for the simple yet effective chemical treatment and/or washing of pulp. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.